The present invention relates to processes and apparatus for measuring the molecular concentration of a constituent in a gas.
The need to determine the proportion of a particular gaseous constituent in a gas arises in various industrial, scientific and medical operations. For example, it is often necessary to determine the proportion of oxygen and/or anesthetic agent in the gas supplied to a surgical patient.
Various means for measuring the proportion of a particular constituent in a gas have been proposed heretofore. As set forth in U.S. Pat. Nos. 4,257,777 and 4,049,383, the amount of light produced by a chemiluminescent reaction involving the constituent of interest is measured and the proportion of the constituent is determined from the measured amount of light. The concentration of a particular gas constituent may also be measured by monitoring the changes in conductivity of a semiconductor resulting from the absorption of the constituent on the semiconductor surface, as disclosed in U.S. Pat. No. 4,495,793. Spectrophotometric measurements, thermal conductivity measurements, and the like have also been employed for measuring the concentration of a particular constituent.
Many of the prior methods and apparatus respond slowly, and hence cannot provide accurate measurements during rapid changes in gas composition. The prior methods and apparatus typically require careful technique and delicate or expensive instrumentation. Moreover, the methods and apparatus utilized heretofore typically have provided only a transitory output signal representative of the concentration of the constituent of interest. Thus, to obtain a permanent record of the concentration, it has been necessary to record the output signal utilizing additional equipment such as electronic recording apparatus. Such apparatus adds complexity and cost and can also introduce error in the recorded readings.